EP1560390A1 - Adaptive control of the bandwidth of a carrier recovery loop in presence of local oscillator phase noise - Google Patents

Adaptive control of the bandwidth of a carrier recovery loop in presence of local oscillator phase noise Download PDF

Info

Publication number
EP1560390A1
EP1560390A1 EP20040290224 EP04290224A EP1560390A1 EP 1560390 A1 EP1560390 A1 EP 1560390A1 EP 20040290224 EP20040290224 EP 20040290224 EP 04290224 A EP04290224 A EP 04290224A EP 1560390 A1 EP1560390 A1 EP 1560390A1
Authority
EP
European Patent Office
Prior art keywords
pll
phase
value
phase error
bandwidth
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP20040290224
Other languages
German (de)
French (fr)
Inventor
Massimo Brioschi
Roberto Valtolina
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Alcatel Lucent SAS
Original Assignee
Alcatel CIT SA
Alcatel SA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Alcatel CIT SA, Alcatel SA filed Critical Alcatel CIT SA
Priority to EP20040290224 priority Critical patent/EP1560390A1/en
Publication of EP1560390A1 publication Critical patent/EP1560390A1/en
Withdrawn legal-status Critical Current

Links

Images

Classifications

    • HELECTRICITY
    • H03BASIC ELECTRONIC CIRCUITRY
    • H03LAUTOMATIC CONTROL, STARTING, SYNCHRONISATION, OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
    • H03L7/00Automatic control of frequency or phase; Synchronisation
    • H03L7/06Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
    • H03L7/08Details of the phase-locked loop
    • H03L7/085Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
    • H03L7/093Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using special filtering or amplification characteristics in the loop
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0014Carrier regulation
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0014Carrier regulation
    • H04L2027/0044Control loops for carrier regulation
    • H04L2027/0053Closed loops
    • H04L2027/0055Closed loops single phase
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0014Carrier regulation
    • H04L2027/0044Control loops for carrier regulation
    • H04L2027/0063Elements of loops
    • H04L2027/0069Loop filters
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04LTRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00Modulated-carrier systems
    • H04L27/0014Carrier regulation
    • H04L2027/0044Control loops for carrier regulation
    • H04L2027/0071Control of loops
    • H04L2027/0079Switching between loops
    • H04L2027/0081Switching between loops between loops of different bandwidths

Abstract

A method for adaptively controlling bandwidth of a carrier recovery loop in radio transmission systems, wherein the phase error in a PLL is adjusted to a minimum level by means of a loop filter incorporated in said PLL. The phase noise value in the local oscillator is determined and the value of the additive white gaussian noise in the PLL is estimated. These values are applied in a predetermined mathematical relationship indicative of the phase error in said PLL in such a manner to determine the bandwidth of the PLL that corresponds to the minimum value of the phase error.

Description

    FIELD OF THE INVENTION
  • The present invention relates to a radio transmission system. More particularly the invention relates to a circuit and a method for the control of the bandwidth of a carrier recovery loop in such radio transmission systems.
  • BACKGROUND OF THE INVENTION
  • In order to make efficient use of the microwave radio spectrum, state-of-art digital point-to-point radio systems employ highly bandwidth-efficient modulation techniques. At present, certain known commercial systems employ 128 QAM signal constellation, nevertheless some 512 QAM prototypes are currently being field-tested. For the sake of clarity it is to be noted that "QAM" stands for Quadrature Amplitude Modulation which is a well known amplitude modulation scheme in which amplitude modulation is performed by two separate signals of two sinusoidal carriers having the same amplitude and frequency but being in phase quadrature, the modulated signals are then added for transmission on a single channel.
  • As the number of the points of the signal constellation grows, the system becomes more sensitive to all types of linear and nonlinear signal distortion. A particularly critical issue in bandwidth-efficient QAM systems is the phase noise (PN) of the local oscillators (LO) which are used to convert the modulated signal from IF to RF and vice versa. Together with other noise-like degrading effects, LO - phase noise (LOPN) gives rise to a constant irreducible bit error rate (BER) independently from the power of the received signal.
  • There are two ways known in the related art to face the problem of LOPN. The first known method is to achieve low noise local oscillators. However, the higher the radio frequency is, the more difficult it is to design and to produce a local oscillator with low phase noise. The second known solution is to choose a demodulation process which is somehow non sensitive towards PN.
  • Consequently the first solution may become considerably expensive, taking into account in particular the fact that at present the radio frequencies that are being used are growing higher and higher in value (e.g. up to 90 GHz).
  • Nevertheless, the second solution can be implemented with phase locked loop (PLL). In fact the PLL principle has been successfully used for decades for tracking the carrier phase. There is plenty of literature available to the public on PLL design and techniques. As a non limiting example reference is made to Floyd M. Gardner, "Phaselock Techniques", Second Edition, John Wiley & Sons.
  • In the context of the above problem, the bandwidth of the PLL is the main parameter to take under consideration. The wider the bandwidth is, the better the demodulator ability becomes in order to track LOPN.
  • However, there are two particular limits in achieving wide bandwidth for the PLL. One such limitation is the introduction of an additional source of phase noise which is due to the phase estimator error introduced by the modulated signal itself; this additional phase noise - that depends also from the quality of the received signal level and from the amount of the additive white gaussian noise (AWGN) - must, as much as possible, remain much lower than the original one. The second limit is the loop electrical delay. It turns out that a long loop electrical delay makes it impossible to go beyond a certain bandwidth, because the phase transfer function of the PLL approaches levels close to instability.
  • From the above discussion it is clear that in order to reach an optimum design of the PLL, its bandwidth and its transfer function depend on the amount of LOPN as well as on the amount of the AWGN.
  • The "standard" solution for achieving the above objectives would be to design a PLL with a fixed bandwidth as wide as possible. However, taking into account that the optimum bandwidth of the PLL depends on the signal to noise ratio of the received signal, then the choice of a fixed bandwidth cannot be considered an "optimum" solution because the signal to noise ratio can change depending on the circumstances.
  • SUMMARY OF THE INVENTION
  • It is therefore an object of the present invention to overcome the above mentioned prior art drawbacks. This objective is achieved by the solution proposed by the present invention according to which by means of adaptively changing the transfer function of the PLL according to the signal to noise ratio (SNR) of the received signal, the BER of the system is improved. In fact, based on knowing the LOPN and estimating the amount of AWGN, it becomes possible to adaptively find the best bandwidth of the PLL, leading eventually to a substantial improvement in BER values.
  • Accordingly it is an object of the present invention to provide a method for adaptive control of bandwidth of a carrier recovery loop in radio transmission systems, said system comprising a local oscillator and a phase locked loop - PLL - for tracking a carrier phase, the PLL having a transfer function, characterized in that a phase error in the PLL is adjusted to an optimum level by means of a loop filter incorporated in said PLL, said optimization of the phase error in the PLL comprising the steps of:
  • a- determining a first value relative to phase noise in the local oscillator;
  • b- estimating a second value relative to additive white gaussian noise in the PLL;
  • c- applying the said first and second values in a predetermined mathematical relationship representing the phase error value as a function of a transfer function value in said PLL; and
  • d- selecting a value of the PLL transfer function corresponding to an optimum phase error value according to said predetermined mathematical relationship.
  • According to an aspect of the present invention, said optimum phase error value is a minimum value.
  • Another object of the present invention is that of providing a system for performing adaptive control of bandwidth of a carrier recovery loop in radio transmission systems, comprising a local oscillator and a phase locked loop - PLL - for tracking a carrier phase, characterized in that the PLL comprises a loop filter incorporated therein for adjusting a phase error in the PLL according to the steps of the method above.
  • These and further features and advantages of the invention are explained in more detail in the following description as well as in the claims with the aid of the accompanying drawing.
  • BRIEF DESCRIPTION OF THE DRAWING
  • The single figure is a block diagram showing a basic scheme of a PLL for use in the solution of the present invention.
  • DESCRIPTION OF A PREFERRED EMBODIMENT
  • There are various known arrangements for PLLs, however, without loss of generality, it can be considered that the basic structure of a PLL can be represented in the block diagram of the figure wherein the PLL circuit comprises a phase detector 1, a loop filter 2, a voltage controlled oscillator 3 and an optional pure delay 4, the latter representing the undesired effect of a delay present in the loop, for example, due to a decision delay in a decision feedback loop. Furthermore the additional source of phase noise is modeled by µ(k) which, as mentioned further above, is due to the phase estimator error introduced by the modulated signal itself, depending also from the amount of AWGN.
  • The input Φ(z) to the phase detector 1 is the difference between two signals, namely an input signal having a phase Θi(z) and an output signal fed-back to the input of the phase detector 1 having a phase Θo(z).
  • In the following, for the sake of simplicity, it is assumed that the system is already equalized and frequency-synchronized, and that both timing recovery and relative gain control have been established. Under the above assumptions, the baud-rate samples rk of the received signal, as it is know in the related art can be expressed as: rk = ak · e +jϕi(k) + nk where ak is a complex number representing the QAM symbol transmitted at time kT, wherein T is represents time in the expression 1/T which is the signaling rate and k is an integer corresponding to the "k"th symbol; ϕ i denotes the unknown phase and nk are the noise samples of AWGN.
  • Reference to the relationship (1) above, can be found among other available literature, in H. Meyr, M. Moeneclaey, S. A. Fetchel, "Digital Communication Receivers", John Wiley & Sons, 1998, page 341.
  • The PLL open loop z-transform transfer function is shown below (equation 2). This is also a known and conventional formula in the techniques related to PLLs: in a simplified interpretation it may be said that this formula is the multiplication of the transfer function of each of the blocks shown in the figure: L(z)= K · F(z) · z - N 1-z -1
  • In the above, L(z) represents the PLL open loop transfer function, K is the phase detector gain, i.e. the slope of the S-curve of the phase detector in the origin , F(z) is the transfer function of the loop filter and N represents the number of symbols in time delay. It is further to be noted that the open loop delay is expressed as NT, shown in the figure by reference numeral 4, wherein T represents symbol time.
  • Reference to the above relationship (2) may be found in H. Meyr, M. Moeneclaey, S. A. Fetchel, "Digital Communication Receivers", John Wiley & Sons, 1998, pages 342-343 and 97-117.
  • The solution according to the invention is based on designing a loop filter 2, which is capable of minimizing the phase error variance σ2 e , subject to the following data and constrains:
  • The power of the AWGN samples nk is represented by σ2 n ;
  • the power spectral density of the phase noise ϕ i (k) is represented by S ϕ(f); where (f) is frequency. It is assumed that nk and ϕ i (k) are uncorrelated.
  • K is the phase detector gain which is a fixed value but only known to belong to an interval K ∈ [K 1,K 2], this parameter reflects the sensitivity of the S-curve of the phase detector to signal to noise ratio;
  • The phase error variance is thus expressed as follows:
    Figure 00080001
  • Here again, reference to the above relationship (3) may be found in H. Meyr, M. Moeneclaey, S. A. Fetchel, "Digital Communication Receivers", John Wiley & Sons, 1998, pages 342-343 and 97-117.
  • As can be noted from (3), increasing the loop bandwidth, the first term increases, related to AWGN contribution represented by σ2 n while the second term decreases, related to phase noise contribution as represented by Sϕ (f). This equation shows clearly the fact that the phase error, and consequently the optimum bandwidth are a function of phase noise and additive white gaussian noise.
  • Therefore, knowing the phase noise of the local oscillator (LOPN) and estimating the amount of additive white gaussian noise, it is possible to adaptively find the best bandwidth that results in the minimization of equation (3), leading eventually to a great improvement in BER curves. This is done by obtaining the value of the transfer function of the PLL corresponding to the minimum value obtained for the phase error.
  • It is to be noted that the mathematical relationship shown in equation (3) above is only an example provided in this description for a clear understanding of the solution provided by the invention. The scope of the invention is not to be construed as to be limited only to the above mathematical relationship. Those skilled in the related art would realize that other mathematical expressions can also be used in order to obtain the desired values of the PLL bandwidth according to the invention.
  • The main advantage of the new solution is that, at every symbol time, the "optimum" PLL transfer function can be found and used, thus obtaining in this manner an improvement in BER.
  • In order to estimate the power of the additive white gaussian noise σ2 n various strategies exist from which, without loss of generality, we can mention the estimation of the Mean Square Error (MSE), that is a direct measurement of the amount of additive white gaussian noise.
  • At this point the minimization of equation (3) can be done in different ways: in a preferred but not limiting embodiment, the optimum value for and, as a consequence, the optimum value for F(z), can be found by direct calculation or it can be found by making use of pre-calculated lookup tables.
  • The cost function to be minimized can be depicted by means of other known expressions as a results of applying different models or different simplifications, within the scope of the solution proposed by the present invention, which is based on providing a radio transmission system with an adaptive bandwidth of the carrier recovery loop.

Claims (4)

  1. A method for adaptive control of bandwidth of a carrier recovery loop in radio transmission systems, said system comprising a local oscillator and a phase locked loop - PLL - for tracking a carrier phase, the PLL having a transfer function, characterized in that a phase error in the PLL is adjusted to an optimum level by means of a loop filter incorporated in said PLL, said optimization of the phase error in the PLL comprising the steps of:
    a- determining a first value relative to phase noise in the local oscillator;
    b- estimating a second value relative to additive white gaussian noise in the PLL;
    c- applying the said first and second values in a predetermined mathematical relationship representing the phase error value as a function of a transfer function value in said PLL; and
    d- selecting a value of the PLL transfer function corresponding to an optimum phase error value according to said predetermined mathematical relationship.
  2. The method of claim 1 wherein said optimum phase error value is a minimum value.
  3. The method of claim 1 or 2 wherein the predetermined mathematical relationship representing the phase error value as a function of a transfer function value in said PLL is expressed as follows:
    Figure 00120001
    wherein:
    σ2 e represents phase error variance;
    σ2 n represents power value of additive white gaussian noise samples;
    (f) represents power spectral density of the phase noise, where (f) is frequency;
    T represents symbol time;
    K represents linearized phase detector gain; and
    L(f) represents the transfer function of the PLL at frequency f.
  4. A system for performing adaptive control of bandwidth of a carrier recovery loop in radio transmission systems, comprising a local oscillator and a phase locked loop - PLL - for tracking a carrier phase, characterized in that the PLL comprises a loop filter incorporated therein for adjusting a phase error value in the PLL according to the steps of the method of any one of claims 1 to 3.
EP20040290224 2004-01-28 2004-01-28 Adaptive control of the bandwidth of a carrier recovery loop in presence of local oscillator phase noise Withdrawn EP1560390A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP20040290224 EP1560390A1 (en) 2004-01-28 2004-01-28 Adaptive control of the bandwidth of a carrier recovery loop in presence of local oscillator phase noise

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP20040290224 EP1560390A1 (en) 2004-01-28 2004-01-28 Adaptive control of the bandwidth of a carrier recovery loop in presence of local oscillator phase noise
US11/043,205 US7443929B2 (en) 2004-01-28 2005-01-27 Method and circuit for adaptive control of the bandwidth of a carrier recovery loop in radio transmission systems

Publications (1)

Publication Number Publication Date
EP1560390A1 true EP1560390A1 (en) 2005-08-03

Family

ID=34639482

Family Applications (1)

Application Number Title Priority Date Filing Date
EP20040290224 Withdrawn EP1560390A1 (en) 2004-01-28 2004-01-28 Adaptive control of the bandwidth of a carrier recovery loop in presence of local oscillator phase noise

Country Status (2)

Country Link
US (1) US7443929B2 (en)
EP (1) EP1560390A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010126844A1 (en) * 2009-04-26 2010-11-04 Qualcomm Incorporated Jammer detection based adaptive pll bandwidth adjustment in fm receiver
CN104283552A (en) * 2014-05-06 2015-01-14 浙江大学 Dynamic phase-locked loop bandwidth adjusting method for carrier extraction

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7702059B2 (en) * 2005-02-09 2010-04-20 Analog Devices, Inc. Adaptable phase lock loop transfer function for digital video interface
CN104521176B (en) 2012-02-28 2018-07-24 英特尔公司 The dynamic optimization of carrier auxiliary performance for communication system

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1115237A1 (en) * 1998-09-18 2001-07-11 Kabushiki Kaisha Kenwood Radio digital signal receiver
WO2001080511A1 (en) * 2000-04-17 2001-10-25 Atmel Corporation Phase noise and additive noise estimation in a qam carrier recovery circuit

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU472567B2 (en) * 1972-01-20 1976-05-27 National Aeronautics And Space Administration Improved narrowband fm system for voice communications
JPH06132816A (en) * 1992-06-08 1994-05-13 Sony Tektronix Corp Phase lock loop circuit
US5832041A (en) * 1994-10-21 1998-11-03 Philips Electronics North America Corporation 64 QAM signal constellation which is robust in the presence of phase noise and has decoding complexity
US6577690B1 (en) * 1998-06-25 2003-06-10 Silicon Automation Systems Limited Clock recovery in multi-carrier transmission systems
US6091303A (en) * 1999-04-06 2000-07-18 Ericsson Inc. Method and apparatus for reducing oscillator noise by noise-feedforward
US7912145B2 (en) * 2003-12-15 2011-03-22 Marvell World Trade Ltd. Filter for a modulator and methods thereof

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1115237A1 (en) * 1998-09-18 2001-07-11 Kabushiki Kaisha Kenwood Radio digital signal receiver
WO2001080511A1 (en) * 2000-04-17 2001-10-25 Atmel Corporation Phase noise and additive noise estimation in a qam carrier recovery circuit

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
OELLERMANN T ET AL: "Performance evaluation of a coded CDMA optical system" MILITARY COMMUNICATIONS CONFERENCE, 1996. MILCOM '96, CONFERENCE PROCEEDINGS, IEEE MCLEAN, VA, USA 21-24 OCT. 1996, NEW YORK, NY, USA,IEEE, US, 21 October 1996 (1996-10-21), pages 908-912, XP010204032 ISBN: 0-7803-3682-8 *

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2010126844A1 (en) * 2009-04-26 2010-11-04 Qualcomm Incorporated Jammer detection based adaptive pll bandwidth adjustment in fm receiver
CN102405600A (en) * 2009-04-26 2012-04-04 高通股份有限公司 Jammer detection based adaptive pll bandwidth adjustment in fm receiver
US8437721B2 (en) 2009-04-26 2013-05-07 Qualcomm Incorporated Jammer detection based adaptive PLL bandwidth adjustment in FM receiver
CN102405600B (en) * 2009-04-26 2014-11-26 高通股份有限公司 Jammer detection based adaptive PLL bandwidth adjustment in FM receiver
CN104283552A (en) * 2014-05-06 2015-01-14 浙江大学 Dynamic phase-locked loop bandwidth adjusting method for carrier extraction
CN104283552B (en) * 2014-05-06 2017-07-28 浙江大学 A kind of method that PLL loop bandwidth for carrier extract is dynamically adjusted

Also Published As

Publication number Publication date
US7443929B2 (en) 2008-10-28
US20050169418A1 (en) 2005-08-04

Similar Documents

Publication Publication Date Title
US20180041370A1 (en) Methods And Apparatus For Synchronization In Multiple-Channel Communication Systems
US9974025B2 (en) Channel-sensitive power control
Petrovic et al. Effects of phase noise on OFDM systems with and without PLL: Characterization and compensation
US6018556A (en) Programmable loop filter for carrier recovery in a radio receiver
US8498352B2 (en) Symmetrical data signal processing
US7149266B1 (en) Signal receiver and method of compensating frequency offset
US7397300B2 (en) FSK demodulator system and method
US7457366B2 (en) System and method for adaptive phase compensation of OFDM signals
US6904098B1 (en) Linear phase robust carrier recovery for QAM modems
US7499508B2 (en) Method and apparatus for adjusting the gain of an if amplifier in a communication system
CA2046399C (en) Equalizer for radio receive signal
US7675983B2 (en) Mitigation of DC distortion in OFDM receivers
US5440587A (en) Demodulator for digitally modulated wave
CA2475895C (en) Process for providing a pilot aided phase recovery of a carrier
Colavolpe et al. Reduced-complexity detection and phase synchronization of CPM signals
US8149976B2 (en) Precise frequency estimation of short data bursts
US5875215A (en) Carrier synchronizing unit
KR100257962B1 (en) Receiver circuit having adaptive equalizer with characteristics determined by signal envelope measurement and method therefor
US7009932B2 (en) Frequency tracking device for a receiver of a multi-carrier communication system
US8860467B2 (en) Biased bang-bang phase detector for clock and data recovery
US7609772B2 (en) Apparatus and method for optimally compensating for imbalance between in-phase and quadrature-phase in a zero-IF OFDM receiver
US7778357B2 (en) COFDM demodulator
EP1528683A2 (en) Digital-data receiver synchronization method and apparatus
US7272175B2 (en) Digital phase locked loop
JP2004531168A (en) Method and system for compensating for carrier frequency offset

Legal Events

Date Code Title Description
AK Designated contracting states:

Kind code of ref document: A1

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PT RO SE SI SK TR

AX Extension of the european patent to

Countries concerned: ALLTLVMK

17P Request for examination filed

Effective date: 20051202

AKX Payment of designation fees

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LI LU MC NL PT RO SE SI SK TR

RAP1 Transfer of rights of an ep application

Owner name: ALCATEL LUCENT

17Q First examination report

Effective date: 20110727

RAP1 Transfer of rights of an ep application

Owner name: ALCATEL LUCENT

18D Deemed to be withdrawn

Effective date: 20120207